High potassium? Check your antibiotic

Jul 01, 2010

Older adults taking the antibiotic combination trimethoprim-sulfamethoxazole (TMP-SMX)—widely prescribed for urinary tract infections—are at increased risk of elevated potassium levels, called hyperkalemia, according to a study appearing in an upcoming issue of the Clinical Journal of the American Society of Nephrology (CJASN). "We found a significant risk of severe hyperkalemia associated with TMP-SMX," comments Matthew A. Weir, MD (London Health Science Centre).

The study was based on 300,000 older adults in Ontario, Canada, who were taking beta-blockers—a widely used class of blood pressure drugs. From this group, the researchers identified 189 patients who were hospitalized for severe hyperkalemia shortly after starting TMP-SMX or other antibiotics commonly used for urinary tract infections.

"Hyperkalemia is a potentially deadly adverse drug reaction, and TMP-SMX is one of the most commonly prescribed antibiotics in North America," Weir explains. "TMP-SMX can decrease the kidney's ability to remove potassium from the body. Potassium plays an important role in regulating heartbeat, and severe episodes of hyperkalemia can cause fatal disturbances in the heart rhythm."

Patients receiving TMP-SMX were more likely to develop dangerously high potassium levels, the study found. Weir says, "The risk of severe hyperkalemia is five times higher in patients prescribed TMP-SMX compared to those prescribed amoxicillin—another popular antibiotic to treat simple bladder infections."

Very few of the patients taking TMP-SMX underwent subsequent blood testing of their potassium level. "Increasing this type of testing represents an avenue to potentially decrease the risk of hyperkalemia associated with TMP-SMX," Weir adds.

Beta-blockers and TMP-SMX can interact, so the researchers had suspected that patients taking both drugs would be at increased risk of hyperkalemia. However, the increase in hyperkalemia with TMP-SMX did not appear any greater in patients who were also taking beta-blockers.

In conducting the study, the researchers used the extensive Ontario health administrative databases. "Without the use of this powerful resource, quantifying this adverse drug reaction would not have been possible," says Weir.

The study had some important limitations—as in all observational studies, the patients were not randomly assigned to different antibiotics. "Also, data regarding factors that can predispose to hyperkalemia, such as diet and levels of physical activity were not available to us," notes Weir. He points out that the results may not be applicable to younger patients.

More information: The article, entitled "Beta-Blockers, Trimethoprim-Sulfamethoxazole, and the Risk of Hyperkalemia Requiring Hospitalization in the Elderly: A Nested Case-Control Study will appear online at doi:10.2215/CJN.01970310

Related Stories

For more than half a century, products containing ion exchange resins have been used in patients with dangerously high levels of potassium. However, there is no convincing evidence that these products are actually effective, ...

Researchers at the University of Maryland School of Medicine have made an important discovery about why potassium builds up to dangerous levels in the bloodstream, a relatively common medical problem that affects about eight ...

For patients with kidney disease on dialysis, the widely used heart medication digoxin may lead to an increased risk of premature death, according to a study appearing in an upcoming issue of the Journal of the American So ...

Johns Hopkins researchers have discovered that a drop in blood potassium levels caused by diuretics commonly prescribed for high blood pressure could be the reason why people on those drugs are at risk for developing type ...

The widely used cancer drug bevacizumab may cause severe loss of protein from the kidney into the urine that can lead to significant kidney damage and can compromise the efficacy of cancer treatment, according to a study ...

A leading association for U.S. pharmacists adopted a policy Monday that discourages its members from providing drugs for use in lethal injections—a move that could make carrying out such executions even harder for states ...

New estimates suggest that 20 to 30 percent of opioid analgesic drugs prescribed for chronic pain are misused, while the rate of opioid addiction is approximately 10 percent, reports a study in the April issue of Pain, the of ...

The nation's largest health insurer, UnitedHealth, will muscle up for its fight against rising prescription drug costs by spending more than $12 billion to buy pharmacy benefits manager Catamaran Corp.